1. Field of the Invention
The present invention relates to a liquid ejection apparatus, an inkjet system, and a flushing method.
2. Description of the Related Art
An inkjet recording apparatus, which is known as one type of liquid ejection apparatus, is an apparatus configured to eject ink as recording liquid onto a recording medium from nozzles of a recording head to form an image on the recording medium. In this type of apparatus, some nozzles may less frequently eject ink depending on image data. The nozzles with low ejection frequency cause a phenomenon that ink remains in the nozzle part to be thickened and abnormality occurs in ink ejection to cause non-ejection of ink and abnormal landing of ink. In order to avoid such a phenomenon, processing called “flushing” for discharging thickened ink is performed. Flushing is classified into line flushing for performing flushing between printing pages and star flushing for performing flushing during a printing page.
As technology for performing such flushing operation, for example, a technique described in Japanese Unexamined Patent Application Publication No. 2015-058556 (Patent Literature 1) is publicly known. In an inkjet recording apparatus disclosed in Patent Literature 1, flushing operation with ink is controlled on the basis of conveyance speed. This inkjet recording apparatus is configured to change at least one of the ejection amount of ink, the ejection speed of ink, ejection liquid droplets of ink, the amplitude of a waveform of a signal for controlling the ejection of ink, the number of inputs of the waveform, the type of the waveform, or the pulse width of the waveform.
In the case where line flushing or star flushing is performed alone, however, it is difficult to maintain print quality under certain conditions. Line flushing is a method of discharging thickened ink with as small an ink consumption amount as possible, and needs to be performed in as small a region as possible in the conveyance direction. Thus, when an image forming region in the conveyance direction is large, the discharged amount of ink needs to be increased and the thickened ink cannot be discharged for a certain period of time, with the result that abnormal landing of ink occurs at the end of the image forming region.
Star flushing is a method of ejecting ink sparsely in an image forming region irrespective of the image forming region, to discharge thickened ink. Star flushing enables a larger amount of thickened ink to be discharged by increasing the ejection amount of ink. When the ejection amount of ink is increased, however, scumming becomes conspicuous and a printed image becomes dirty. In particular, scumming is more conspicuous on a sheet such as coated paper. If the number of ink droplets necessary to discharge thickened ink is ejected, the printed image deteriorates more depending on the type of sheet.
In other words, line flushing involving ejecting ink between printing pages has a problem in that when an image forming region of a page in the conveyance direction is large, a printed image deteriorates at the end of the image forming region. Star flushing involving ejecting ink in an image forming region has a problem in that when the ejection amount of ink is increased, dirt becomes conspicuous to deteriorate printing quality.